On Wed, 22 Apr 1998, Andre Fachat wrote: > Does that work with indexed access as well? I vaguely remember that with some indexed or indirect addressing, I was able to get the wrong number, maybe off by one. But it was a very long time ago, and I don't remember this very well. Let's see what happens with LDX#$80:LDA $2080,X, with PC initially $1000: 1000 a2 1001 80 1002 bd 1003 80 1004 20 2000 20* 2100 20* The data marked with * is what remains from the last valid bus access on the bus. > If it is the second one, I assume it's something to do with capacitance, > i.e. the internal (input) pullups cannot get the lines high in time > without active (output) NMOS pullups. The signal lines have a capacitance > and the together with the resitors you get an exponential rise with > tau ~ (R * C). This could be the explanation. Most C64s are not "de00 compatible", i.e. reading from $de00-$dfff will not directly reflect the data read by the video chip on the previous halfcycle. It's again a very long time ago, but I think that all the errors with "de00 incompatible" C64s I tested were so that a bit was set while it shouldn't be. Hmm, to make the computer more "de00 compatible", you will need to add some capacitors to the bus. Or just use a very long ribbon cable on the cartridge port. :-) Marko
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